Comparisons of topical and spray applications of two pesticides, triazophos and jinggangmycin, on the protein content in the ovaries and fat bodies of the brown planthopper Nilaparvata lugens Stål (Hemiptera:Delphacidae)

https://doi.org/10.1016/j.pestbp.2014.06.008Get rights and content

Highlights

  • Protein content in ovaries and fat bodies of BPH for TZP and JGM sprays was higher than that for their topical treatments.

  • No significant difference in protein content was observed between JGM topical treatment and control.

  • JGM foliar spray application should be reduced to avoid pest resurgence.

Abstract

The pesticide-induced stimulation of reproduction in pests is one of the most important mechanisms of pest resurgence. There have been numerous reports on the insecticide-induced stimulation of reproduction. However, the relationship between pesticide application method and pest resurgence (stimulation of reproduction) has received little attention. Here, we studied the effect of two treatment methods, triazophos (TZP) and jinggangmycin (JGM), on the protein content in the ovaries and fat bodies of the brown planthopper (BPH) Nilaparvata lugens Stål. The results showed that pesticide treatment methods significantly affected the protein content in the ovaries and fat bodies of BPH. In addition, grand means (means of main effect) of the protein content at 2 and 3 days after emergence (2 and 3 DAE) for foliar sprays was significantly higher than that observed after topical treatments, which increased by 23.9% (from 1.42 to 1.76) and 8.82% (from 4.42 to 4.81), respectively. No significant differences on the protein content in the ovaries and fat bodies for the JGM topical treatment were observed compared with controls. However, the protein content for JGM foliar sprays was significantly higher than that for the controls. The protein contents in both topical and spray treatments of TZP were significantly higher than those of the controls. Ovarian protein is mainly yolk protein. There is a positive correlation between ovarian protein content and the number of eggs laid. These findings show that foliar spray of the pesticides promotes the resurgence of BPH. Therefore, the foliar spray of some pesticides, such as JGM, should be avoided for the control of pests, which is the sideeffects of the fungicide on non-target insect pests’ occurrence.

Introduction

The brown planthopper (BPH) Nilaparvata lugens Stål, is a classic pest whose resurgence is induced by pesticides. The mechanisms of pesticide-induced resurgences of pests are involved in the stimulation of reproduction [1], [2], [3], [4] and the destruction of their natural enemies [5], [6]. Pesticides stimulate the reproduction of pests by increasing the protein and RNA content in the ovaries and fat bodies of adult females. The protein and RNA contents in the ovaries and fat bodies have been shown to increase linearly with insecticide concentrations and days after emergence (DAE) when three insecticides triazophos (TZP), deltamethrin and imidacloprid, were applied [7]. The genes associated with reproduction were up-regulated expressions [4], [8]. In addition, insecticides significantly enhanced the protein content (including sperms) of male accessory glands (MAGs) after 40 ppm TZP and 12 ppm deltamethrin treatments [8], [9]. For example, the protein content of MAGs after 40 ppm TZP and 12 ppm deltamethrin treatments was doubled compared with that of control males [10]. Interestingly, the effect of insecticides on the reproduction of BPH males can be transferred to females via mating [11]. Experiments showed that a greater quantity of MAG products of insecticide-treated adult males was transferred to adult females via mating [10] and resulted in an increase of the number of eggs laid of females [11]. Furthermore, changes in the biochemistry and physiology of rice plants induced by the foliar spray of pesticides also are one mechanism underlying the stimulation of BPH reproduction [1]. For example, foliar sprays of TZP, jinggangmycin (JGM; a fungicide), and imidacloprid significantly decreased the oxalic acid content of rice plants [12]. Rice plants treated with pesticides are beneficial to the feeding and survival of BPH [1]. In addition, whether pesticides stimulate BPH reproduction may depend on the treatment method. For example, the number of eggs laid by BPH females that have experienced JGM foliar sprays is significantly greater than that of eggs laid by BPH that have experienced a topical treatment [4]. Thus, the treatment methods have important implications for pests. The methods used in numerous pesticide toxicology experiments, including the pesticide-induced stimulation of reproduction, are either topical or spray tests. However, the effects of topical and foliar spray applications of pesticide on protein content of the ovaries and fat bodies in BPH have not been investigated.

Physiologically, the number of eggs laid is affected by the synthesis of yolk protein in the fat body. However, the yolk protein content is also influenced by nutritional and environmental conditions. Thus, the protein content in fat bodies of the adult females is a physiological index for the degree to which reproduction is stimulated by insecticides. Variation in the fat body and ovary proteins shows the same tend. Here, we compared the effects of two treatment methods (topical application and foliar spray) of two pesticides on the protein content of the ovaries and fat bodies in BPH.

We selected TZP and JGM not only because the organophosphate TZP is a classic insecticide that stimulates the reproduction of BPH [2], [3], [13], but also because recent studies have shown that TZP enhances the thermotolerance of BPH [14]. JGM, an antibiotic compound developed in China, is a fungicide that is mainly used to control the rice sheath blight Rhizoctonia solani in China. The fungicide is commonly applied two or three times during rice growth by foliar spray at the commercial rate of 125–175 g.a.i.ha−1 (approximately 200–300 ppm). The objective of this study was to compare the effects of different pesticide treatment methods on the protein content of the ovaries and fat bodies in BPH.

Section snippets

Rice variety, insects, and pesticides

The rice (Oryza sativa L.) variety Ningjing 2 (japonica rice) was used in each trial. This variety of rice was selected because it is commonly planted in Jiangsu Province, China. Seeds were sown outdoors in standard rice-growing soil in cement tanks (height 60 cm, width 100 cm, and length 200 cm). When seedlings reached the 6-leaf stage, they were transplanted into plastic pots (30 cm diameter, 30 cm height), with 4 hills per pot and 4 plants per hill. The rice plants used in the experiments were at

Effects of topical and spray treatments of TZP and JGM on protein content in the ovary of BPH

The ANOVA of the data presented in Fig. 1 showed that the pesticides and the treatment methods significantly influenced protein content in the ovaries of BPH (Table 1). Grand means (means of main effect) of protein content in the ovary at 2 and 3 DAE in the foliar spray treatments were significantly greater than those observed for the topical treatments, which increased by 23.9 (from 1.42 to 1.76) and 8.82% (from 4.42 to 4.81), respectively. For both pesticides, grand means of protein content

Discussion

Here, we showed that the foliar spray of TZP and JGM promoted the synthesis of protein in the ovaries and fat bodies of BPH females. The protein content in the ovaries and fat bodies after the spray treatment was significantly higher than that observed after the topical treatment, especially the spraying of JGM. The above findings have important implications for the study of the physiological and ecological mechanisms of pest resurgence and for pest management because foliar spraying is one of

Acknowledgments

This research was partially funded by The National Nature Science Foundation of China (31371938), the Ph.D. Advisor Fund of the Ministry of Education of China (No. 20123250110008), and Jiangsu Province Agricultural Fund for Independent Innovation (CX(14)2025).

References (20)

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